Decadal stability of Red Sea mangroves

Study Number

94

Author

Hanan Almahasheer, Abdulaziz Aljowair, Carlos M. Duarte, Xabier Irigoien

Abstract

Across the Earth, mangroves play an important role in coastal protection, both as nurseries and carbon sinks. However, due to various human and environmental impacts, the coverage of mangroves is declining on a global scale. The Red Sea is in the northern-most area of the distribution range of mangroves. Little is known about the surface covered by mangroves at this northern limit or about the changes experienced by Red Sea mangroves. We sought to study changes in the coverage of Red Sea mangroves by using multi-temporal Landsat data (1972, 2000 and 2013). Interestingly, our results show that there has been no decline in mangrove stands in the Red Sea but rather a slight increase. The area covered by mangroves is about 69 km2 along the African shore and 51 km2 along the Arabian Peninsula shore. From 1972 to 2013, the area covered by mangroves increased by about 0.29% y -1. We conclude that the trend exhibited by Red Sea mangroves departs from the general global decline of mangroves. Along the Red Sea, mangroves expanded by 12% over the 41 years from 1972 to 2013. Losses to Red Sea mangroves, mostly due to coastal development, have been compensated by afforestation projects.

Main Results and Conclusions

• The Red Sea mangroves grow in a different environment than many of the rest of the world’s mangroves.
  • “Along the Red Sea, mangroves experience some of the most difficult conditions in their distribution range, including no permanent freshwater inputs, salinities over 40 ppt, sea surface temperatures over 31 C in summer and recent abrupt warming of the sea…” (164)
• Anthropogenic interference to Red Sea mangroves is relatively limited.
  • “…urban development and aquaculture in the Red Sea are comparatively limited and, because the desert nature of the coast, direct anthropogenic impacts have been relatively contained.” (164)
• There was an increase of mangrove cover from 1972 to 2000, but no significant increase between 2000 to 2013.
  • “The estimated total area of Red Sea mangroves increased significantly… from 120 ± 0.54 km2 in 1972 to 132 ± 0.94 km2 in 2000, and no significant change, within the power of our analysis, was detected between 2000 and 2013… when the area was estimated at 135 ± 0.86 km2…” (167)
  • “We identified about 5000 mangrove patches along the Red Sea (2234 in 1972, 5765 in 2000 and 5157 in 2013).” (167)
• The study concludes that there were no major losses of mangroves along the Red Sea, in part because of active afforestation projects.
  • “Although Red Sea nations are also experiencing population growth 1.8-5.1% per annum (PERSGA, 2002), our analysis did not provide evidence of major losses of mangrove stands over the past four decades. On the contrary, the areas covered by Red Sea mangrove stands increased significantly, by 15 Km2 (11 Km2 when excluding the patches too small to have been detected in 1972), or 12%, during the study period.” (168)
  • “This expansion is the net result of the balance between losses and gain, where afforestation projects have played an important role in maintaining, and expanding mangroves along the Red Sea.” (170)
• Coastal development has the potential to threaten Red Sea mangroves in the future.
  • “However, coastal development in the region, including major infrastructure projects for ports and tourism, may represent a threat in the future unless mangrove conservation receives prominent attention as a required milestone at the planning stage.” (170-171)